Just so I'm 100% sure exactly why one would choose 64 or 128. So it's an environment based decision and not hardware based? ie: I would pick 128k over 64k because of how big the files I am working with(video)...nothing to do with the model of the hard drive requuiring a certain block size.?

A larger block size means less reading to the drive so performance is improved even more? Then why not crank it all the way up to 512k or more?

Just so I'm 100% sure exactly why one would choose 64 or 128. So it's an environment based decision and not hardware based? ie: I would pick 128k over 64k because of how big the files I am working with(video)...nothing to do with the model of the hard drive requuiring a certain block size.?

A larger block size means less reading to the drive so performance is improved even more? Then why not crank it all the way up to 512k or more?

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What you are saying is generally correct as far as my understanding. However, I base my recommendations on tests I've done and what I've read others have done. The optimal block size does seem to vary and if you want the best performance you need to test it with your own system. Meaning format it with 32k and run the AJA, BlackMagic or other speed tests (depending on your hardware) write down the numbers, then try a different block size. Keep doing that until you tried them all and find out for yourself. For me it was the 128k block size by a narrow margin. The 32k and 64k were acceptable on my system as well.

It's been awhile and I don't really remember where I read the outcome of other peoples tests, but you might try searching the obvious Cow forms to see if you can get anymore insight. The Apple discussions Xserve RAID forum might have some info as well, but they erase old posts, so it would have to be something fairly recent.

Also, you might want to speak with AJA, BlackMagic, etc to see what they recommend. I use Xserve RAID's and there maybe a hardware difference (I run RAID 50, over Fibre, and the size of my storage considerably bigger as well.

So no specific answers, either test and pick what gives you the best numbers, accept a general recommendations, or ask the capture card manufacturer what they believe is best.